In the microfabrication using a resist composition, with an increase in the integration degree of an integrated circuit, formation of an ultrafine pattern is required. To meet this requirement, the exposure wavelength tends to become shorter, such as from g-line to i-line or further to excimer laser light, and, for example, development of a lithography technique using an electron beam is proceeding at present. As the formed pattern becomes finer, thin film formation of the resist film is also proceeding so as to prevent a problem of pattern collapse. With respect to the resin used in a resist composition for forming a conventional resist film as thick as having a film thickness of 0.2 to 1.0 μm, a resin having an acetal structure where a hydrogen atom of a phenolic hydroxyl group is replaced, for example, by an acid labile group containing a specific ring structure is described in JP-A-2000-239538 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-2006-146242 and International Publication No. 05/023880.
In order to form an ultrafine pattern, thin film formation of the resist is necessary, but this incurs deterioration of the dry etching resistance. Also, in electron beam lithography, the effect of electron scattering (forward scattering) in the resist film is recently reduced by increasing the accelerating voltage of the electron beam (EB). However, in this case, the electron energy trapping ratio of the resist film decreases, giving rise to reduction in the sensitivity, and the effect of scattering (back scattering) of electrons reflected in the resist substrate increases. Above all, in the case of forming an isolated pattern having a large exposure area, the effect of back scattering is large, and the resolution of the isolate pattern is impaired.
Particularly, in the case of patterning on a photomask blank used for semiconductor exposure, a light-shielding film containing a heavy atom is present below the resist, and the effect of back scattering attributable to the heavy atom is more serious. Therefore, in the case of forming an isolated pattern on a photomask blank, among others, resolution is highly likely to be decreased.
As one of the methods to solve these problems, use of a resin having a polycyclic aromatic skeleton such as naphthalene is being studied (see, for example, JP-A-2008-95009 and JP-A-2009-86354), but the problem about the resolution of an isolated pattern is unsolved. In JP-A-2005-99558, as one of the methods to enhance the resolution of an isolated pattern, a resin containing a group for adjusting the solubility is used, but the resolution of an isolated pattern has not yet reached a satisfactory level.
Also, the microfabrication using a resist composition is not only used directly to produce an integrated circuit but also applied, in recent year, to the fabrication or the like of a so-called imprint mold structure (see, for example, JP-A-2008-162101 and Yoshihiko Hirai (compiler), Nanoimprint no Kiso to Gijutsu Kaihatsu•Oyo Tenkai—Nanoimprint no Kiban Gijutsu to Saishin no Gijutsu Tenkai (Basics and Developments of Technology and Application of Nanoimprint—Fundamental Technology of Nanoimprint and Deployment of Leading-Edge Technology), Frontier Shuppan (issued June, 2006)). Therefore, it becomes an important task to satisfy high sensitivity, high resolution property (for example, high resolution, excellent pattern profile and small line edge roughness (LER)) and good dry etching resistance all at the same time, and this needs to be solved.